Trailers for transporting standardized containers have numerous designs and have been adapted for many specific purposes in the prior art. U.S. Pat. No. 3,034,825 describes a typical trailer designed for container transport. As shown in that patent, the forward end of the trailer is raised relative to the rest of the trailer in a goose-neck design.
The goose-neck allows the trailer to clear the fifth wheel of the tractor while allowing the trailer to be lower to the ground for stability, and to allow, within regulatory overall height limits, high cube containers for maximum cubage (volume). However, as shown in the above-identified patent, the long standardized containers of 40' must lie on the raised portion as well as the lowered portion in order to meet highway length requirements. This requires a tunnel well in the forward part of the container so that it mounts on the trailer in a horizontal position.
Trailer designs for standardized 20' containers are likewise found in the prior art; however, the standardized 20' container has no tunnel well for accommodating a goose-neck portion of a trailer.
Trailers today which specifically receive 20' containers often have no goose-neck at all. The complete trailer bed is flat and lies at a level which clears the fifth wheel of the tractor. This trailer need only be slightly over 20' since the container rides on the portion of the trailer above the fifth wheel.
Heavily loaded 20' containers pose an additional problem. It is possible with certain cargo to load over 48,000 lbs. into a single 20' container. A load of this size, however, requires that the trailer bogie and the tractor bogie be separated lengthwise by more than the length of 20' feet in order to conform to applicable highway regulations. When conventional 40' flatbeds are used the center of gravity for the load is raised, and since flatbeds are significantly heavier than this skeletal container transporter (chassis) cargo weight is penalized.
This raised center of gravity can result in a relatively unstable container trailer. This is especially true when the container is heavily loaded. Furthermore, the level of the trailer bed required to clear a typical fifth wheel is above the nominal level of a loading dock and the floor of the container is elevated by approximately 6" from the floor of this flatbed trailer. Thus the trailer requires two loading ramps for loading or unloading the container, one for the flatbed, and one for the container. The ramps must necessarily angle upward, making loading and unloading difficult.
The prior art has also acknowledged the benefit of a goose-neck design to lower the center of gravity of the container even when the container does not ride over the forward portion but rather rests completely on the lowered portion. U.S. Pat. Nos. 3,587,890 and 2,772,892 are examples of such designs. The latter device also acknowledged the benefit of distributing the load rearwardly and is specifically designed for stabilizing the ride for heavy containers.
Finally, the prior art container trailers have a number of built-in, retractable loading ramps to facilitate loading and unloading of the trailer. Many of these devices in their operational position simply angle down from the rear of the trailer to the ground. These devices would also interfere with cargo stored on the trailer in their retracted position. U.S. Pat. Nos. 3,424,323 and 1,699,882 are examples of such devices.
The prior art therefore lacks a trailer specifically adapted for hauling a heavily loaded standardized 20' container which has a lowered center of gravity, has the weight of the container distributed over a relatively long trailer section and which has a platform designed to facilitate the loading and unloading of the container while being non-obtrusive when the container itself is being removed or mounted on the trailer bed.